Calcium oxide (CaO) is commonly used in water softening and precipitation of hardness from water supplies and occasionally in waste water treatment. Less commonly, calcium oxide (CaO) is used for the treatment of sludges such as municipal sewage sludge, sea or river bottom sludge which may be contaminated with PCB's or industrial waste sludges.
Methods of transforming sludge into ecologically acceptable solid materials by using calcium oxide (CaO) are well known from, for example, U.S. Pat. No. 4,079,003 issued Mar. 14, 1978 to Frank Manchak, Jr. Briefly, that patent teaches mixing intimately mixing calcium oxide (CaO) with sludge having a water content of not over about 78% by weight in a confined space whereby an exothermic reaction takes place with consequent rise of temperature and pH which substantially deactivates bacteria and pathogenic organisms and results in a solid, friable and substantially odor free reaction product.
U.S. Pat. No. 4,270,279 issued Jun. 2, 1981 to Roediger teaches that intimate mixing of calcium oxide (CaO) and sludge need not take place so long as the exposed surfaces of dewatered sludge particles are dusted with calcium oxide (CaO) to form a granular product which can be used as fertilizer.
Although the reaction product resulting from the sludge treatment process disclosed in U.S. Pat. No. 4,079,003 is ecologically acceptable due to the specific conditions required in the process, substantial amounts of calcium oxide (CaO) are required with attendant expense. Also, any residual organisms present in the reaction product which are still active can result in odors and the need for further treatment such as incineration.
We have now discovered improved methods of treatment of sludge with calcium oxide (CaO) or, for the first time to our knowledge, with calcium carbide (CaC.sub.2), wherein calcium oxide (CaO) can be reclaimed from the reaction product while the reaction product is exposed to a final incineration step so that a substantial portion of re-claimed calcium oxide (CaO) can be repeatedly recycled in the process. The resulting amount of reaction products to be disposed of is less than 10% of the weight of the wet sludge.
As defined herein, the term "sludge" is intended to encompass any and all types of sludge including, without limitation, municipal sewage sludge, riverbottom sludges, industrial waste sludges and contaminated soils such as found in hazardous waste disposal sites which may be contaminated with toxic metals, PCB's, etc. to which water may be purposely be added so as to give the contaminated soil a relative high moisture content so that the contaminated soil essentially attains the physical characteristics of common sludges.
The primary object of the invention is to economically and rapidly decompose sludge with simultaneous recovery and recycling of substantial portions of the treatment chemical used in the process.